The present disclosure relates to semiconductor device manufacturing, and more particularly to a method to minimize edge-related substrate breakage during spalling.
Surface layer removal from brittle substrates using controlled spalling technology is promising to be a powerful method for changing the cost structure of high-efficiency photovoltaic materials, as well as enabling new features in a range of semiconductor technologies (e.g., flexible photovoltaics, flex circuits and displays). Cornerstone to this technology is the application of a tensile stressor layer on the surface of a base substrate to be spalled. The tensile stressor layer has a combined thickness and stress that is sufficient to induce spalling mode fracture in the base substrate. Such a spalling process is disclosed, for example, in U.S. Patent Application Publication No. 2010/0311250 to Bedell et al.
Experimentation in spalling seems to indicate that it is a critical phenomenon; given a sufficiently high thickness and stress value in the tensile stressor layer, spalling mode fracture occurs spontaneously. There is, however, a reasonably large process window of metastability. Stressor thickness and stress combinations that are unstable against spalling mode fracture will be “nucleation-” or “initiated-limited”.
Handling layers that are applied to the surface of the stress/substrate combination are then used to control the initiation and fracture propagation leading to the removal of continuous surface layers from the base substrate.
Spalling offers a low cost, simple approach for removing many thin semiconductor layers from a comparatively expensive thick base substrate. In order to maximize the reuse of the base substrate, it is important to minimize wafer breakage or any uncontrolled fracture in the stressor layer/base substrate system.